1. Field of the Invention
The present invention relates to a light source dimming control circuit, and more particularly, to a light source dimming control circuit for dimming a light source between an analog dimming mode and a pulse width modulation dimming mode.
2. Description of the Prior Art
As related technologies improve, various types of light sources, such as light emitting diodes (LEDs) or cold cathode florescent lamps (CCFLs) are applied to various types of illumination devices for purposes of power-saving. The LED light source is a current controlled light source, where brightness of the LED light source is related to a current level of a driving current. Generally, the LED light source can dimmed according to a pulse width modulation method or an analog method.
When in a pulse width modulation dimming mode, a switch is turned on and off interlacedly according to a duty ratio of a pulse width modulation signal, for generating a discrete current as the driving current of the LED light source. Although the pulse width modulation dimming mode can provide better accuracy for controlling the driving current of the LED light source, but the electro-magnetic interference (EMI) also increases as the current level of the driving current getting higher.
When in an analog dimming mode, analog components, such as resistors and capacitors are utilized to generate a continuous current as the driving current of the LED light source. Although the analog dimming mode can reduce the EMI interference, but inaccuracy of the driving current is enlarged by tolerances of the analog components as the current level of the driving current getting lower.
Therefore, it is required to provide a mechanism, which keeps both of the advantages of the analog dimming mode and the pulse width modulation dimming mode, and avoids both of the disadvantages of the analog dimming mode and the pulse width modulation dimming mode.